The present invention relates to electronic postage meters, and more particularly to a dual redundant electronic postage meter for increasing the reliability of the meter operation.
Various electronic postage meter systems have been developed, see for example, the systems disclosed in U.S. Pat. No. 3,978,457 for Microcomputerized Electronic Postage Meter Systems, U.S. Pat. No. 3,938,095 for Computer Responsive Postage Meter, European Patent Application 80400603.9, filed May 5, 1980, for Electronic Postage Meter Having Improved Security and Fault Tolerance Features, U.S. Pat. No. 4,301,507, for Electronic Postage Meter Having Plural Computing Systems, and co-pending application Ser. No. 447,815, filed Dec. 8, 1982, for Stand-Alone Electronic Mailing Machine, now U.S. Pat. No. 4,579,054.
Generally electronic postage meters include some form of non-volatile memory capability to store critical postage accounting information. This information includes, for example, the amount of postage remaining in the meter for subsequent printing and the total amount of postage already printed by the meter. Other types of accounting or operating data may also be stored in the non-volatile memory, as desired.
However, conditions can occur in electronic postage meters where information stored in non-volatile memory may be lost. A total line power failure or fluctuation in voltage conditions can cause the microprocessor associated with the meter to operate erratically and either cause erasure of data or the writing of spurious data in the non-volatile memory. The erasure of data or the writing of spurious data in the non-volatile memory result in a loss of critical accounting information. Since the accounting data changes with the printing of postage and is not permanently stored elsewhere, there is no way to recapture or reconstruct the lost accounting information. Under such circumstances, it is possible that a user may suffer a loss of postage funds.
To minimize the likelihood of a loss of information stored in the non-volatile memory, various approaches have been adopted to insure the high reliability of electronic postage meters. It is known from aforementioned U.S. Pat. No. 3,978,457 and aforementioned co-pending application Ser. No. 447,815, now U.S. Pat. No. 4,579,054 to provide a microprocessor controlled electronic postage meter having memory architecture which includes a temporary storage memory for storing accounting data reflecting each meter transaction and a non-volatile memory to which the accounting data is transferred during the power down cycle of the meter.
Another approach for preserving the stored accounting data has been the use of redundant non-volatile memories. One such redundant memory system is disclosed in patent application Ser. No. 343,877, filed Jan. 29, 1982, in the name of Frank T. Check, Jr., and entitled Electronic Postage Meter Having Redundant Memory, now abandoned in favor of application Ser. No. 723,001, filed Apr. 15, 1985 which issued on Jan. 21, 1986 as U.S. Pat. No. 4,566,106. With such redundant memory system the two redundant non-volatile memories are interconnected with a microprocessor by way of completely separate data and address lines to eliminate error conditions. The data stored in each memory is the same, although the data may be stored in a different form in each memory, e.g., it may be coded. The data is applied to the memories simultaneously or sequentially at different times during the postage transactions.
Another redundant memory system is disclosed in the aforementioned European Patent Application 80400603.9. In such patent application, the same accounting data is written into each of the two non-volatile memories, designated BAMs, by updating the specific registers of the BAMs twice during each postage meter transaction, once in temporary form and once in permanent form to minimize the loss of accounting data during microprocessor failure.
Pending patent application Ser. No. 643,113 filed Aug. 22, 1984 and entitled, Electronic Postage Meter Having Multiple Non-Volatile Memories For Storing Different Historical Information Reflecting Postage Transactions, now U.S. Pat. No. 4,731,749, disclosed a first non-volatile memory having cumulative historical information of postage transactions written therein during the power down cycle of the meter and a second non-volatile memory having a greater data storage capacity than the first non-volatile memory for sequentially writing historical information regarding each trip cycle of the meter in a different address in the second non-volatile memory in real time as each postage transaction occurs so that two different records of historical information regarding the postage transactions are provided.
Pending patent application Ser. No. 643,112 filed on Aug. 22, 1984, and entitled Memory Address Location System For An Electronic Postage Meter Having Multiple Non-Volatile Memories, now U.S. Pat. No. 4,627,016, discloses a non-volatile memory for storing data in which data is used to locate the next memory address in which to write data in another non-volatile memory.
However, although the aforementioned systems have contributed to increased meter reliability, occasions may occur during meter operation when it is desirable to provide increased meter reliability. For example, if there is microprocessor failure and/or a failure of both NVMs.
This invention deals both with the primary function "accounting" arithmetic process, and data storage by providing for redundant microprocessors and memory means. The methodology described allows for detecting and locating source of critical process and data storage errors. Consequently dual redundancy within a module and dual redundant modules provides a significant increase in meter reliability.